A. Field of the Invention
The present invention relates to a precipitation polymerization process for producing an oil adsorbent polymer in the form of unit micro-particles, aggregates and agglomerates of micro-particles capable of entrapping any desired oleophilic solid and/or oleophilic liquid compound for delivery. More particularly, the present invention relates to a process for producing a highly porous and highly cross-linked pleophilic polymer in the form of individual micro-particles; aggregates of micro-particles; and clusters of aggregates (agglomerates) of micro-particle spheres characterized by a unit particle size of about 0.1 to about 100 microns, preferably about 0.1 to about 80 microns, preferably having a mean particle size of about 5 to about 12 microns and an oil sorbency of at least about 80% by weight or greater, based on the weight of adsorbed oil plus micro-particle adsorbent polymer. The present invention is also directed to the assemblies of oil adsorbent micro-particle aggregates produced by the process having sizes up to about 3000 microns preferably less than about 1000 microns. The micro-particles produced by the process of the present invention have extremely low apparent bulk densities in the range of about 0.02 gm/cc to about 0.1 gm/cc, preferably about 0.03 gm/cc to about 0.07 gm/cc, more preferably about 0.03 gm/cc to about 0.04-0.05 gm/cc. The micro-particles produced by the process of the present invention are capable of holding and releasing oleophilic oils, creams, cleaners, medicaments and other organic active compounds and compositions, for use in the cosmetic, cleaning, chemical process and pharmaceutical industries.
B. Background
Early disclosures of polymer particles appear in U.S. Pat. Nos. 3,493,500 and 3,658,772, which issued on Feb. 3, 1970 and Apr. 25, 1972, respectively. They teach the production of aqueous suspensions of polymer particles from acrylic acid monomer and/or acrylamide monomer in an aqueous reaction medium at pH 1-4. Both patents teach that the resultant polymer suspensions, which were not characterized as to particle size or structure, were suitable for use as flocculating agents for sewage treatment.
It was subsequently discovered that polymers could be made in a porous particulate form by a variety of techniques. The art has stated that xe2x80x9cthe type of polymerization technique used is an important factor in the determination of the resulting product.xe2x80x9d See U.S. Pat. No. 4,962,170 at column 2, line. 4. As stated in the ""170 patent at column 2, lines 7-11, xe2x80x9cwithin each type of polymerization, there are procedural alternatives which can have significant impact on the resulting productxe2x80x9d xe2x80x9c[t]he differences in the polymerization techniques are enough that a procedure used in one type of polymerization technique that will not necessarily have the same effect if used in another polymerization technique.xe2x80x9d Thus, there is a significant degree of unpredictability in the art.
Porous polymeric particles are capable of being prepared by one of two processesxe2x80x94precipitation polymerization in a single solvent system, or suspension polymerization in a two phase liquid system. The precipitation polymerization technique is presented in U.S. Pat. Nos. 4,962,170 and 4,962,133 both of which issued on Oct. 9, 1990. The ""170 patent discloses a precipitation polymerization process wherein the disclosed monomers are soluble in the single solvent system, whereas the resulting polymer, which is insoluble, precipitates out of solution once a critical size is obtained. In the ""170 process, the solution of monomer consists exclusively of one or more types of polyunsaturated monomer. Because each monomer is polyunsaturated, each monomer also functions as a cross-linker, resulting in a highly cross-linked polymer particle.
Like the ""170 patent, the ""133 patent also utilizes the precipitation polymerization process for producing a porous polymeric particle. However, unlike the ""170 process, wherein the monomer solution consists exclusively of polyunsaturated monomers, the ""133 process discloses the monomer solution may include one monosaturated monomer in combination with one polyunsaturated monomer, wherein the polyunsaturated monomer may comprise up to 90% by weight of the total weight of monomers. Because the precipitation polymerization technique relies upon the formation of polymer aggregates of precipitated polymer particles, the monomer solution is not vigorously agitated during polymerization to avoid separation of the aggregated polymer particles.
U.S. Pat. No. 5,316,774 is directed to a suspension polymerization process, again limited to a maximum of 90% by weight polyunsaturated monomers based on the total weight of monomers. Accordingly, it is an object of the present invention to provide a process for making sorbent micropolymers from a monomer solution that contains more than 90% by weight, preferably about 92% to 100% polyunsaturated monomers, by weight based on the total weight of monomers in the monomer solution.
The ""133 process is limited to a solvent system that is an aqueous/organic azeotrope. Because the organic solvent cannot be separated from the water in an azeotrope, azeotropic solutions present special waste disposal problems. Accordingly, it is an object of the present invention to provide a process for making oil adsorbent micropolymers that does not require an azeotropic solution. Further, the particles produced by the ""133 process range extensively in size from less than about 1 micron in average diameter for unit particles to about twelve hundred microns in average diameter for clusters of fused aggregates. The large variability in size limits the utility and properties of the polymeric particles. Accordingly, it is also an object of the present invention to provide a process for making polymeric micro-particles of a less diverse size distribution.
Another process disclosed in the art for producing microscopic polymers is in situ suspension polymerization wherein an active ingredient included within the monomer mixture is retained in the formed polymer upon completion of polymerization. Examples of in situ suspension polymerization include U.S. Pat. No. 4,724,240 wherein polymerization of a monounsaturated monomer and a polyunsaturated monomer in an aqueous/polyvinylpyrrolidone system containing an emollient, as the active agent, produced only relatively large micro-particles, having a mean diameter xe2x80x9cbetween 0.25 to 0.5 mmxe2x80x9d (250 to 500 microns) that contains the emollient therein upon completion of polymerization. A problem with a particle having a mean diameter of 250-500 microns is that the particle is capable of being sensed by touch. This is an undesirable property if the particle is to be used in a lotion or cream or other cosmetic formulations. Accordingly, it is also an object of the present invention to provide a process that is capable of manufacturing polymeric particles having a smaller mean diameter, e.g., 0.5 xcexcm to 120 xcexcm, for a smoother skin feel; as well as aggregates and assemblies of aggregates capable of entrapping oleophilic solids and viscous liquids.
A second problem with the process of the ""240 patent is that it is limited to those active ingredients that are capable of dissolving in the organic solvent. The polymeric micro-particles of the present invention are capable of adsorbing organic compounds and organic compositions containing hydrophobic compounds dissolved in an organic solvent, as well as solid organic compounds entrapped within an interior of an open center of an aggregated cluster of micro-particle spheres. Further, the active ingredient(s), which may be proprietary, must be provided in bulk to the polymer manufacturer so that they may become trapped in the particles during the polymerization process. To overcome these problems, it is a further object of the present invention to provide polymeric micro-particle aggregates having an evacuated internal volume, defined within a continuous string or cluster of aggregated micro-particle spheres, that are capable of adsorbing and entrapping hydrophobic solids and fluids, within the interior surface area of each open sphere, in large amounts so that they may be loaded within the interior volume surrounded by the micro-particle spheres with adsorbed active hydrophobic organic ingredient(s) in solid or solvent-dissolved form, and loaded on the exterior surface area of the aggregated spheres with any hydrophilic compound, in solid form or as an organic solvent-based viscous solution or dispersion.
A third problem with the ""240 process is that it is not suited for use when the active ingredient is a mixture of components that differ significantly from one another as to lipophilicity. In such a situation, the more lipophilic of the active ingredients would be selectively isolated in the pores of the polymer made by the ""240 process. To overcome this problem, the ""240 process would have to be separately applied to each of the active ingredients, and thereafter, the resulting products would be mixed. However, such additional processing and mixing is costly. Accordingly, it is a further object of the present invention to provide a process for producing a aggregates of micro-particles wherein the micro-particle aggregate is capable of adsorbing a plurality of organophilic active ingredients.
It was unexpectedly discovered that the process of the present invention is capable of producing micro-particles and micro-particle aggregates that have a high compound absorbency for oleophilic compounds, and can be manufactured in a variety of particle size distributions by a precipitation polymerization process.
The present invention is directed to a process for making a porous polymer aggregate formed from a plurality of micro-particles that exhibits a high oil absorbency. The method of the present invention comprises the steps of:
dissolving at least one and preferably at least two polyunsaturated monomers, preferably also an effective amount of an organic polymerization initiator, in a water-immiscible organic solvent and a silicone solvent that is inert (not reactive) with respect to-the monomers and resulting polymer to provide a monomer mixture; in the preferred embodiment, the silicone solvent also acts as a solvent so that a separate solvent is not needed;
continuing agitation at a rate that does not break the aggregates into smaller aggregates or individual spheres, for example, using a tip speed for a rotating paddle impeller of about 0.1 to 0.2 meters per second up to about 15 meters per second, e.g., 30 rpm, during polymerization of the monomers in the suspended micro-droplets to produce microporous polymer micro-particles, and micro-particle aggregates in the form of aggregated spheres having an interior void volume surrounded by the aggregated spheres; and
separating the microporous polymer micro-particle aggregates from the organic solvent to produce microporous, oil adsorbent polymer micro-particles having a diameter of about 0.1 to about 100 microns, preferably about 0.1 to about 80 microns. The aggregates, or assemblies of micro-particles, can be manufactured to have diameters of about 1 to about 500 xcexcm and new and unexpected adsorptive capacity for oleophilic compounds, in both solid and liquid forms. Preferably more than 99% of the aggregates and agglomerates are smaller than 500 xcexcm, preferably less than about 100 xcexcm.
The present invention is further directed to microporous, oil adsorbent micro-particles and micro-particle aggregates of a polymer comprising at least one and preferably at least two polyunsaturated monomers, the micro-particles and micro-particle aggregates characterized by having a void volume surrounded by aggregated micro-particle spheres and having a mean unit micro-particle diameter of less than about 10 microns, preferably less than about 8 microns, having a total adsorption capacity for organic liquids, e.g., mineral oil that is at least 80% by weight, preferably at least about 85% by weight, based on the total weight of adsorptive micro-particles plus adsorbed oil. In a preferred embodiment, the micro-particle assemblies, or aggregated spheres of micro-particles of the present invention are characterized by a mean unit diameter from about 5 to about 500 microns, preferably about 5 xcexcm to about 100 xcexcm, some aggregates having a diameter of about 2 to about 100 xcexcm, others having diameters from about 20 to about 80 microns.